Twenty Thousand Leagues Under the Sea meets Frankenstein by the Costa Award-winning author of The Lie Tree. 'One of our finest storytellers,' Sarah Perry, author of The Essex Serpent This macabre YA adventure, with a touch of Lovecraftian steampunk, features underwater exploration, monsters of the deep, relic-based technology and questions of loyalty. The gods are dead. About fifty years ago they turned on one another and tore each other apart. Nobody knows why. In an alternative world, fifty years after the death of the gods, a fifteen-year-old boy, Hark, finds the still beating heart of a terrifying deity and uses it to try to save his best friend. Hark risks everything to keep the heart out of the hands of smugglers, military scientists and secret fanatical cults, to try to use it to sustain the life of his best friend, who is gradually and eerily transforming. But how long should someone stay loyal to a friend who is himself becoming a monster?